As colorful as the rainbow and as sparkling as fine leaded crystal,
gemstones have captured the imaginations and desires of men and (perhaps
especially) women for ages. The pursuit of gems have become the subject
of legends, fairy tales, epics, and major motion pictures ("Romancing
the Stone", for one). Today, more fine gemstone specimens are available
to the average person than at any time in history.

What makes a gemstone?

Generally speaking, a gemstone is a stone that
is beautiful, rare, and durable (resistant to abrasion, fracturing and
chemical reactions). Some minerals can be very beautiful, but they may
be too soft and will scratch easily (such as the mineral
fluorite).
Fluorite is extremely colorful and pretty but has a hardness of only 4 on
the Moh's hardness scale and has four perfect
cleavage directions, which
makes it only an oddity as a cut gem.
Others are too common and are given a semi-precious status (such as
agate).
Most gemstones have good hardness (above 5) and a high
index of refraction (the higher the index of refraction the greater the sparkle).
All gemstones have some characteristics
falling short of perfection though; even the seemingly perfect Diamond has four
directions of cleavage. Note that the most common mineral in the Earth's crust is quartz, with a hardness of 7. Since quartz is everywhere (especially in common dirt and dust), any material that is softer may be scratched during ordinary wear.

Most gems are silicates which can be very stable, hard minerals. A few gems are
oxides and only one gem, diamond, is composed of a single element, carbon. There
are also many gemstones that are not true minerals, but which are gemstone
varieties of recognized minerals. In most cases, these variety names are historical, as the gemstones were not recognized as being varieties of other minerals until well after the name was in common use
(such as aquamarine, emerald, and heliodor as varieties of beryl).
Often, new names will be created for ordinary sounding minerals which sound prettier or more valuable, such as "Moldavite" for the green variety of tektites.
In some cases, the names are true misnomers, such as "Green Amethyst" for
prasiolite (a transparent green variety of quartz).

A few gemstones are mineraloids (not true minerals) and are included
below: opal, amber, and moldavite. Pearls
don't even qualify as mineraloids, as they are not only the result of an organic
process plus they are properly composites, containing both the mineral aragonite
and the protein conchiolin.

While almost any mineral can be cut in
the manner of a gemstone, below is a list of some of the gem kingdom's
more prized and recognized members.

What makes a Precious Metal?

Like gemstones, one of the characteristics of a precious metal is its rarity.
It could not be "precious" if it were common! Two other characteristics
are also important. Foremost is durability - it must not easily corrode
away, nor can it be brittle. And that is related to the third
characteristic, ductility. This means that the metal must be malleable,
that it can be bent, hammered, or otherwise shaped. Gold is the most
malleable of metals (it can be hammered into incredibly thin foils or drawn into
extremely fine wires), it does not corrode or dissolve except under the most
extreme conditions. It is so durable that nearly all of the gold ever
mined is still in circulation or storage.